The invention relates to a device for connecting a towed pipe or pipe string to a towing apparatus, for example a percussion boring machine or a towing head, by means of which the towed pipe can be drawn into the ground or into a pre-formed pilot bore in the ground.
In the trenchless laying of pipelines by means of a percussion boring machine and in expanding a pilot bore by means of a towing, displacing, bursting or excavating head the object is to draw in a new product pipe simultaneously with the formation of the bore in the ground or the expansion of a pilot bore. The same applies to the destructive replacement of underground pipelines in which an old pipe is destroyed, for example by means of the chisel head of a percussion boring machine, and the fragments are forced laterally into the ground in order to increase the free cross-section of the underground pipeline so that a towed pipe having a diameter the same as or even larger than that of the old pipe can be drawn in with as little friction as possible at its outer wall.
Usually the new pipe is connected directly to the apparatus which is forming or expanding the bore in the ground, in order to prevent collapse of the bore in the region between the towing apparatus and the new pipe. This is mostly done by means of snap or screw connections.
However, in all methods the towed pipe is subjected to high frictional forces, depending on its length and the nature of the wall of the bore, which are still considerable even if a lubricating suspension, for example a bentonite-water suspension, is used when drawing in the new pipe. Further loadings on the new pipe occur in the case of dynamic drawing in using a percussion boring machine of which the ramming blows can act undamped on the towed or new pipe.
The loads described above make high demands on the connection between the towing apparatus and the new pipe, which usually consists of plastics material, for example HDPE.
While a number of pipe connections are known, these cannot cope with the high loads when pipe lengths of over 100 m and pipe diameters of, for example, 100 to 900 mm, are being drawn into the ground.
Thus European patent specification 0 086 567 discloses a pipe connection for use with a percussion boring machine in the destructive replacement of underground pipelines by means of a conical expander head. This pipe connection serves to connect the new pipe, which in provided with an internal screw thread, to a jacket pipe which is spaced from and surrounds the percussion boring machine and also has an internal screw thread. This is done by means of two intermediate pieces each provided with a screw thread at each end, and requires time-consuming screwing together of the four parts which are to be connected.
However, in the case of pipes of plastics materials problems already arise from the fact that the plastics materials in question have a high coefficient of thermal expansion. The resulting thermal expansions make screwing difficult, depending on the outside temperature.
Further, Swiss patent specification 684 546 describes a pipe connection in which the front pipe end has a smaller diameter and is provided there with an annular groove for a sealing ring. This pipe end engages in the rear end of the leading pipe, the sealing ring snapping into an internal annular groove and thereby wedging the two pipes together. However, since the sealing ring consists of a relatively soft material, this pipe connection can only transmit small tensile forces. Nevertheless the connection is so firm that it is difficult to release it in axe2x80x94usually narrowxe2x80x94trench or in a narrow shaft.
Again, pipe connections are known from British application 2 090 931 and U.S. Pat. No. 5,360,242 in which at least one internal locking rib at the connecting end of a neighbouring pipe engages behind at least one external shoulder at the connecting end of a pipe, and the connecting end leaving the locking rib is clamped between the external shoulder and a further shoulder on the connecting end itself. This gives rise to considerable difficulties in forming the pipe connection owing to the thermal expansion of the plastics materials which come into question for such pipes.
Starting from this state of the art, the object of the invention is to provide a less expensive but stable connection by which a towed pipe can be fastened to a towing apparatus and which in particular is able to transmit high tensile forces even in the case of dynamic boring or expanding of a pilot bore.
To this end, the invention comprises a device having an adapter sleeve for the transition from the towing apparatus to the towed pipe and a towed pipe of which the connecting end is locked to the adapter sleeve. The locking brings the adapter sleeve and the towed pipe into a secure but preferably releasable connection.
More particularly, the connecting end of the towed or new pipe can be provided with at least one groove and the adapter sleeve with at least one complementary rib, or vice versa. The preferably more than one ribs engage in the grooves and are locked there in such a way that the connection is able to meet all the demands of the heavy-duty operation of drawing in pipes.
The locking is preferably effected by means of a locking sleeve which supports the connection of the adapter and the towed pipe in the radial direction on the inside or outside.
Another means of connection in accordance with the invention comprises providing the connecting end and the adapter sleeve with opposed grooves into which preferably releasable locking bars can be pushed, by means of which the adapter sleeve and the towed pipe are locked together. The locking bars can have an insertion bevel and/or a pulling eye in order to facilitate their introduction into the grooves and their removal therefrom. The bars can also have a larger bearing area in the direction of advance than in the opposite direction. To stabilise this kind of connection a supporting sleeve may be provided in the connecting end of the towed pipe, between which and the adapter sleeve the front end of the pipe is then clamped.
The supporting sleeve preferably has a collar which engages between the front end of the towed pipe and a complementary internal shoulder of the adapter sleeve. The external diameter of the pipe in the adapter sleeve is preferably the same as the external diameter of the pipe to be drawn in. The locking bar or bars consist of an elastic material and preferably have a rectangular or square cross-section.
The towed pipe can be connected to the connecting pipe through a electric welding sleeve. Such a sleeve is described in the German Offenlegungsschrift 197 18 790, the contents of which are to be regarded as forming part of the present description. Generally butt welding is also suitable for connecting the pipes or pipe sections.